*{margin: 0;
padding: 0;}
body,html{
    height: 100%;
}
.container{
    background-color: yellow;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
}
.box{
    width: 100px;
    height:100px;
    background-color: red;

}